This invention relates generally to the field of industrial sawing, and more specifically to automatic sawing machines.
Automatic sawing machines are known in the art to possess several automatic or semi-automatic features. Typically, these include (a) automatic advancement of a blade into a workpiece and subsequent retraction of the blade to a home position, (b) automatic actuation of a workpiece shuttle to "pull" a workpiece in the direction of work flow to a sawing position by an indexed length, (c) the automatic opening and closing of stationary and shuttle vises, and (d) a means to cut several pieces to the same length and angle of cut.
Certain saws in the art, notably Armstrong-Blum Manufacturing Company's MARVEL Series 81A , Model 10 and Series 15A, Model 8 metal cutting band saw machines, have in addition a provision to add to each "pull" length a value for saw kerf. This accounts for material lost during the sawing process when calculating what workpiece length should be pulled forward by the workpiece shuttle.
As illustrations of the background state of the art, the reader is directed to Catalog 8103, MARVEL Series 81 & 81A Band Saw Machines, and Publication 81877, MARVEL Series 81 and 81A Parts Catalog, both published by Armstrong-Blum Manufacturing Co. of Chicago, Ill., both incorporated herein by reference.
Many deficiencies have evidenced themselves when employing these prior art methods of sawing. Some deficiencies go to a lack of versatility, others to a lack of precision.
Usually the quantity of pieces to be sawed is set on a mechanical counter. Each time the saw blade rolls forward to perform a cut, a limit switch or other simple means signals the counter to decrement by one count.
The length to be cut is conventionally determined by setting physical stops on the travel of the workpiece shuttle. One of the disadvantages of this procedure is that in the prior art, no more than two fixed length have been settable. A shuttle pull sequence containing more than two different lengths cannot be specified with known prior art saws. In order to effect a cutting plan using variable lengths to minimize waste of a possibly expensive piece of stock, the machine must be stopped and the mechanical stop manually adjusted.
Often it is necessary to cut more than one large piece of stock into relatively small lengths. If the pieces of stock to be cut are separated on a feeding table by a larger distance than the table has been set to move, the table will be unable to "get" the next piece of stock even when the machine is manually operated, without changing the feed length setting. The operator must first remove the previously set inch stop and then manually operate the shuttle to retrieve the next piece.
In the case of known prior art saws having a blade tilt feature, it is conventionally possible to set up such saws to make a series of cuts at up to two angles only. Sawing steps at more than two different angles have not been settable with prior art saws. Partially due to this, known prior art saws typically cannot be set up to automatically perform a sequence requiring more than two cuts at different angles at one place on the workpiece.
Further time is lost in the conventional "automatic" sawing method because, as known in the prior art, the manually set shuttle travel stops and blade tilt offer no opportunity to set up the machine for the next job while the current job is running.
In addition to limitations on time and adaptability, the conventional semi-automatic sawing method has problems obtaining accuracy and precision of saw results. In an industrial environment where increasingly close tolerances are specified and expensive materials are often employed, a lack of accuracy and repeatability can reduce the usefulness of the machine.
Because the shuttle conventionally "bangs" to a stop to index the workpiece pull length, the pull length may change from one repetition to the next. Frequent readjustment may be required, limiting the number of precise repetitions possible.
Repeatability is also affected when the operator chooses to cut a length x, a length y, and a length x again. Because the shuttle travel stop has to be reset before a different length is cut, two cuts of a similar length separated by a different cut will rarely be the same.
As noted above, certain machines are capable of compensating for saw kerf by adding this value to the length of workpiece to be pulled. This method will overcompensate for saw kerf when the saw is set up to bring forward a length of workpiece longer than the maximum shuttle stroke. This is because the saw kerf will be added to each of several shuttle strokes, resulting in the pulling forward of too much material. While this problem can be compensated for by dividing the value used for saw kerf by the number of needed shuttle strokes, an additional manual operation is thereby introduced.
Additional accuracy problems exist when a conventional saw machine has a blade tilt feature. When the blade is tilted from normal for a saw cut, the horizontal component of the saw kerf is a function of the secant of the tilt angle. Where the blade is tilted, therefore, the addition of a unmodified saw kerf value to the shuttle pull length undercompensates for the amount of material lost as measured horizontally.
It has also been found that sawed workpiece length accuracy is adversely affected in saws with a blade tilt feature whenever the axis of blade tilt it not exactly coplanar with the top of the machine table.
It is therefore a general object of the invention to provide a method and apparatus of automatic sawing which is faster, more accurate, more precise and more versatile than conventional methods and apparatus.
A principal object of the invention is to provide a sawing method and apparatus by which a saw program may be specified. The specified program can include a plurality of different sawing lengths and sawing angles. Such a provision obviates the necessity of manually operating the saw when a length or angle is changed.
Another principal object of the invention is to provide a method and apparatus which will saw workpieces with uniform accuracy and precision, regardless of changes in tilt angle, presence of multiple pulls per saw step, number of repetitions, or lack of coplanarity of the pivot axis and the saw table.
A further object of the invention is to provide an automatic saw machine which may be programmed by an operator either before or during machine operation.
Another object of the invention is to provide an automatic sawing method which can be programmed into a sawing machine in a series of saw steps, the user being able to add, change or delete steps after the initial programming.
Another object of the invention is to provide for accurate and precise measurement and control of shuttle movement.
A further object of the invention is to accurately apply a pivot point correction factor to each saw step length in machines having a blade tilt feature.
A still further object of the invention is to allow for the correction of saw kerf in machines having a blade tilt feature.
Another object of the invention is to encode tilt or shuttle incremental motion into signals and provide a method whereby a direction sense is obtained from the signals.
Another object of the invention is to sense and count the beginning and ending of such signals and thereby increase measurement accuracy.
Another object of the invention is to provide an automatic sawing method whereby successive cuts can be made to a workpiece without pulling a further length.
A further object of the invention is to provide a means of stopping an automatic sawing machine during execution of a saw step, the stopping point occurring after the sawing step is completed.
Yet another object of the invention is to provide means to automatically resume a sawing job sequence after such is interrupted.
A still further object of the invention is to accurately sense shuttle position.
Further objects of the invention will be made apparent from the detailed description of an illustrated embodiment which will follow.
In accordance with the invention, an automatic sawing machine is provided. The sawing machine has a programmable controller, an automatic workpiece shuttle with a motion encoder, and in one embodiment a blade tilt mechanism with a motion encoder. The programmable controller is operably connected to the motion encoders, other sensing means and various controlling means as hereinafter described.
The programmable controller is preferably built around an 8-bit microprocessor with bus connections to a keyboard/display, random access memory (RAM), electronically programmable read-only memory (EPROM), electronically programmable and erasable read-only memory (E.sup.2 PROM), memory and input/output selects, counter-timers for receipt of encoder data and interfaces to sensing and enabling peripherals such as limit switches and solid state relays. An optional connection to an external data communications link which would connect the programmable controller to an external source of control, such as a mainframe computer, can also be provided.
Among the solid state relays are those which control operation of the shuttle and machine vises, shuttle motion, tilt motion (where a tilt feature exists), blade motion and the hydraulic pumps.
A buffer interfaces the microprocessor with several mechanical limit switches that provide status and location information on various machine components. In the illustrated embodiment, limit switches detect the presence of the saw blade carriage at either its fully extended or retracted positions, and a limit switch likewise detects the presence of the workpiece shuttle at an extended end of its stroke. Further limit switches react to "out of stock" and "broken blade" conditions.
The tilt and shuttle encoders encode travelled angular and distance increments preferably through use of optical sensors. In the illustrated embodiment, the tilt motion encoder has its detection axis coaxial with and operably connected to the pinion gear affixed to its detection axis, which in turn engages an arcuate rack affixed to the machine table. The shuttle motion encoder is affixed to the shuttle, and has a pinion gear engaging a straight rack affixed to the shuttle table. In both cases, the pinion gear could conceivably be on the stationary element rather than the moving element, but the preferred arrangement is the opposite way.
Each encoder senses movement increments in either direction along their respected gear racks. Upon sensing an incremental displacement, either encoder will send out two signals, both preferably in the form of a quadrature square wave. The first signal or wave will partly precede the second signal or wave if movement is sensed in one direction, and the second signal will partly precede the first if movement is in the other direction.
These signals are received by a clocked register which in turn sends them on to a series of programmable array logic (PAL) chips. The PAL chips are able to distinguish up-count signals from down-count signals according to the order in which they are received by the clocked register. Further, the
and clocked register are able to discern the beginning of a signal from the ending of a signal as separately countable events, thereby providing twice the number of events to count.
Up-counts and down-counts are sent from the PAL to a set of counter-timers, which sum the negative counts and separately sum the positive counts. The microprocessor periodically retrieves these sums and subtracts one sum from the other. In this way, the shuttle and tilt positions are correctly monitored. Down-counts result when the shuttle or tilt mechanism temporarily moves backward due to vibration, and their inclusion in determining the position of the shuttle and tilt mechanism results in accuracies of 0.002 inches and 0.6 minutes of arc.
The E.sup.2 PROM is designed to contain several saw machine setup parameters, most of which are configured at the factory. These include:
saw blade kerf PA1 pivot point correction factor PA1 shuttle creep distance PA1 shuttle stop-look-ahead distance PA1 shuttle signal deadband PA1 tilt creep distance PA1 tilt stop-look-ahead distance PA1 tilt signal deadband
The saw blade kerf may be changed by the machine operator. It is used to calculate the amount of the workpiece needed to be pulled forward to compensate for material lost in the sawing process.
The pivot point correction factor is specified at the factory for machines with a blade tilt feature. It is the perpendicular distance between the plane of the table top and the tilt axis.
The shuttle creep distance represents that distance through which the shuttle will move at a reduced rate of travel toward the end of its stroke.
The shuttle stop-look-ahead distance represents that distance through which the shuttle will coast at the end of its pull stroke under no power.
The column tilt mechanism creep distance, stop-look-ahead distance and signal deadband are specified for similar purposes in those machines having a blade tilt feature. When moving to a new tilt angle, the tilt mechanism will move most of the distance at a normal rate. Toward the end of the movement, the tilt mechanism will creep at a reduced rate.
After initial configuration, the saw is ready to be programmed with one or more sawing jobs. Each job has one or more sawing steps, each step defining a machine operation cycle. A pull-up length, saw angle (in the case of tilt saws) and number of repetitions are the data entered for each saw step. A length of zero can be specified, in which case no further length of stock will be pulled up. These data are entered either by an operator through the programmable controller keyboard or from a main frame through the serial data communications link.
The programmable controller allows step data to be deleted, changed or added at any time in which the affected step is not being run. Other jobs may be programmed, changed or deleted at the same time that the saw is running a previously programmed job. A number of job repetitions is an additional piece of data which can be entered or changed.
One feature of the invention allows the running job to be stopped after the current saw step is completed. This allows the operator to change the job program and perform any necessary manual tasks, after which the job program can be reactivated where it left off.
The operator can program the programmable controller to interpret entered data as being in either English (inches) or metric (millimeters) units. Further, he can tell the controller that all data being entered is metric (or English), except when indicated to the contrary for an indicated job.
The controller will display the current job step being run unless asked to program, change or delete another job or step.
After the operator has programmed one or more jobs, he is ready to run a job. Starting the program will at an appropriate time, cause the blade to begin running. The shuttle vise is caused to open and is commanded to move forward to the saw position, which is declared to be zero. The blade tilt mechanism is commanded to tilt the blade column to the angle for the first step, going through regular tilt rate, creep, stop-look-ahead and deadband phases.
The shuttle is then commanded to retract. The shuttle motion encoder monitors the shuttle motion and communicates signals to the programmable controller for each distance increment moved. The programmable controller calculates a pull length l.sub.1 as either equal to the shuttle stroke (where the desired step pull length is longer than the shuttle stroke, requiring successive shuttle strokes) or a length actually pulled Len.sub.p where: ##EQU1## where k is the kerf value,
Len.sub.s is the desired workpiece length, PA0 h is the table offset (vertical point correction), PA0 .phi..sub.1 is the angle of the first saw cut, PA0 .phi..sub.2 is the angle of the second saw cut.
The microprocessor decrements corrected pull length l.sub.1 as the shuttle retracts down the table.
When decremented l.sub.1 .ltoreq.c, a shuttle creep length, the programmable controller actuates a shuttle slow down relay to reduce the shuttle's rate of movement. When decremented l.sub.1 .ltoreq.h, the shuttle stop-look-ahead-length, the programmable controller turns off the shuttle drive means, allowing the shuttle to coast.
While the shuttle is being retracted or the workpiece is being pulled forward, the controller is also directing the tilting mechanism (in an embodiment which has such) to tilt the blade to the desired saw-angle .phi..sub.s. Tilt movement is monitored and controlled in a manner similar to shuttle movement.
Once the workpiece has been pulled forward in one or more strokes, the controller commands the blade to advance and cut the workpiece. Upon sensing that the cut is complete, the controller commands the saw to retract to home. The shuttle is then rezeroed, and the machine is then ready to perform the next saw step. Execution of the steps continue until the end of the job or until the occurrence of an abnormal condition such as a broken saw blade, in which case operation ceases immediately and an appropriate error message appears on the display.